The present invention relates to a method for manufacturing a lens array optical system comprising two lenses or more.
An example of a conventional method for manufacturing a lens array optical system is described below with reference to FIGS. 5 through 10.
FIG. 5 shows a lens array optical system comprising three plano-convex lenses 1 in the same configuration and a flat glass plate 2. FIG. 5A is a perspective view showing the lens array optical system. FIG. 5B is a plan view showing the lens array optical system of FIG. 5A. FIG. 5C is a side view showing the lens array optical system of FIG. 5A. The lenses 1 and the glass plate 2 are made of BK7 or synthetic quartz commercially available and adhered to each other with a heat-resistant adhesive agent which has a low degree of deformation and is hardened by ultra-violet rays.
The conventional method for manufacturing the lens array optical system as shown in FIG. 5 is described below with reference to FIG. 6.
According to the method, the glass plate 2 is inserted into a concave 13a of a flat glass plate holder 13 as shown in FIG. 6A. Then, a lens holder 14 is placed on the glass plate holder 13 as shown in FIG. 6B. An adhesive agent which has not hardened is applied to the flat surface 1d of the lens 1, and the lens 1 is then inserted into a through-hole 14a formed in the lens holder 14 as shown in FIGS. 6C and 7A, then, pressed against the glass plate 2. That is, the lens 1 is positioned in the lens array optical system by the inner configuration of the through-hole 14a of the lens holder 14 and the outer configuration of the lens 1. Finally, ultraviolet rays are irradiated over the lens 1 to harden the adhesive agent. Then, the glass plate holder 13 and the lens holder 14 are removed from the glass plate 2 and the lens 1. Thus, the lens array optical system is formed.
According to the conventional method as described above with reference to FIGS. 6A through 6D, each lens 1 is positioned in the lens array optical system by the inner configuration of the through-hole 14a of the lens holder 14 and the outer configuration of the lens 1. Then, the flat surface 1d of the lens 1 is adhered to the glass plate 2. Therefore, if a lens 1 is eccentric, the optical axis 5 of the lens 1 is not perpendicular to the glass plate 2. FIG. 8A shows a lens 1 which is not eccentric. FIG. 8B shows a lens 1 which is eccentric, so that the optical axis 5 thereof is not perpendicular to the glass plate 2.
For example, the pitches between the through-holes 14a of the lens holder 14 are designed as p.sub.1 and p.sub.2 as shown in FIG. 9A. Supposing that neither of the lenses 1 is not eccentric, the optical axes 5 thereof is perpendicular to the glass plate 2 and the pitches q.sub.1 and q.sub.2 between focal points 6 thereof are equal to the pitches p.sub.1 and p.sub.2 between the through-holes 14a of the lens holder 14, respectively, as shown in FIG. 9B. Since each lens 1 is actually eccentric, the optical axis 5 thereof is not perpendicular to the glass plate 2. Therefore, the pitches r.sub.1 and r.sub.2 between the focal points 6 thereof are unequal to the pitches p.sub.1 and p.sub.2, which are design values, between the through-holes 14a of the lens holder 14, respectively, as shown in FIG. 9C.
If the thicknesses of the lenses 1 of the lens array optical system are equal to each other, the focal lengths thereof (back focus: d) are equal to each other as shown in FIG. 10A. However, each lens 1 actually has an error in its thickness. Accordingly, the focal lengths (back focus: d+.DELTA.d) of the lenses 1 are different from each other as shown in FIG. 10B.
That is, according to the conventional method for manufacturing the lens array optical system, the optical accuracy of the lens array optical system such as the accuracy of the inclination of the optical axis of the lens 1 and the position of the focal point thereof depends on the processing accuracy of the lens holder 14, namely, the processing accuracy of the through-hole 14a and the processing accuracy of the lens 1, namely, the accuracy of the inclination of the optical axis thereof and the outer configuration and thickness thereof. Therefore, according to the conventional method, it is necessary to produce both of the lens holder 14 and the lens 1 with a high accuracy in order to manufacture a lens array optical system with a high accuracy. In order to manufacture a compact and thin lens array optical system, it is necessary to manufacture a compact and thin lens. But a lens of a high accuracy manufactured by the conventional method is very expensive even though it can be manufactured.